Chick picks: The domestic chick as a model of innate preferences

In this step, entitled Chick Picks we’ll take a look at the domestic chick as the model of innate preferences. Nature or nurture. How much of each? How can we studied this? When studying the well-known nature versus nurture issue, some species of animals are particularly useful. I’m referring to precocial species, those that are completely independent of birth. Those animals are able to move as soon as they are born. a fact that allows us to investigate a newborn individual with the same methodology of an adult one a rare opportunity that we do not have with humans! In the last decades, domestic chicks have become the most prominent model in the study of inborn cognitive abilities.

Chicks don’t need parental care As soon as they hatch, they are able to survive on their own. They can eat and drink on their own and even walk around from the first day of their lives. Their vision is also very good, the right of the shell. In a few words, they are perfect to be tested in this field! I told you the cheeks count for psychologists but in this case I’m referring to chicks’ ability to do simple mathematical calculations. Several studies showed that chicks can add and subtract numerical information in different contexts as many other animals do. Chicks can distinguish between 2 and 3 dots, and they can also count the number of social companions they can see.

Well you know what? People seem to represent numbers as different visuo-spatial forms typically organized along a so-called “mental number line” which is a horizontal continuum oriented from left for smaller numbers to right for larger numbers In short if I asked you “How do you represent numbers?” You might typically respond “as a line, with numbers oriented from left to right”. For decades, psychologists thought it was a cultural phenomenon. We learned to read from left to right therefore, it’s easier for us to represent numbers from left to right. But how sure we are on this? Recently Rugani and colleagues found that a mental number line oriented from left to right is present at birth in a vertebrate brain.

Three-day old chicks were initially trained to find food behind a panel bearing 5 bright spots. Then they were confronted with the two arrays bearing different numbers of spots. When faced with two arrays that had only two spots each the birds consistently looked behind the left of the two panels When faced with eight spots on each panel, they went poking around the right panel. It seems that chicks have an inborn representation of numbers from left to right. Small numbers are represented on the left of the visual field. For this reason, they searched for number 2 on the left, while large numbers are represented on the right Hence they looked for the large numbers on the right visual field.

This is important because if we want to develop a model to study mathematical abilities, we need not only a species that has numerical abilities, but also species with similar mental representation of numbers compared to humans… and domestic chicks seem to satisfy this criterion.

Another thing: People can easily spot if a living organism is in front of them just by observing motion cues, the so-called “biological motion” This can happen even with laboratory stimuli in which the pattern are distilled to just a few animated dots against a black background. We can even tell the gender and the emotional state of an abstract human figure simply by its movement. Because we can discern so much from such a sparse information scientists think specialized neural circuitry is at work. But it is not clear whether the ability is innate or learned. The first response to this issue comes from animal studies. Vallortigara and collaborators took chicks and gave them a choice between two computer screens.

One that showed a dotted animation of a hen walking and one, that showed either a dotted hen shape rotating around an axis or dots moving at random. The chicks preferred to move toward the working hen even though they had never seen a hen before. Interestingly, the chicks didn’t show any preference between the motion of a chick or that of a cat which is a potential predator. This demonstrates an inborn preference for following living organisms ‘per se’. So this is not species-specific. Probably having a species-specific mechanism would have been expensive in term of pre-wired cognitive equipment so animal developed a preference for a general biological motion.

In most of the cases, the first animals close to us as soon as we are born is … our mother. The stimuli used in chicks were later presented to human newborns by Simion and colleagues. Interestingly even newborns looked longer at the walking hen showing a spontaneous preference for the biological motion of a vertebrate. Again, this is not conspecific Babies demonstrated attraction to a working animal, showing that we (like chicks) are not equipped to prefer the movement or our conspecifics. So we can really say the chicks helped pave the way for this important discovery in developmental psychology. Now, let’s have a break and listen to some good music.

Wait, “why” did we find is so good? The kinds of sounds that humans tend to find pleasant are described as consonant which are different from unpleasant sounds, which are called dissonant.

Two-month-old babies prefer to listen to to consonant music rather than dissonant music. So we already know this is found in humans. However, the question remains as to whether the preference for consonant music is fundamental to the properties of the auditory system or if the preference for consonant music is a product of culture or experience. Even though two month old babies haven’t had that much experience with music it is still possible that their preference for consonant music could have developed very fast after birth or even while still in utero.

The best way to test whether or not the preference for consonant music is innate or learned by experience, is through a controlled rearing study in which animals are raised from birth in a controlled environment. It is impossible to raise a human in this way, but it is possible to do this with chicks. And this is exactly what Chiandetti and Vallortigara did. At the end of the testing cage there were two speakers. One speaker played a consonant version of a melody, and the other played a dissonant version of the same melody.

After listening to the sounds for half a minute the chick was given six minutes to approach one of the two sides of the cage while the music continue to play. For the first four minutes of the six-minute testing period The chicks tended to freeze where they had been placed in the center of the testing cage, which is consistent with a natural fear response due to a new situation. However, after calming down during minutes five and six the chicks chose to approach (and spend more time ) on the side of the cage playing consonant music more often than the side playing dissonant music.

By the chick study, we may suppose there is an innate preference for consonant sounds that is independent of experience. These are just some example of the contribution of chicks to the hot topic in psychology on the pre-wired cognitive abilities present at birth in the absence of experience. If you want to listen to another example in which researchers used chicks in this field listen to the podcast by Cinzia Chiandetti “Are you born with a natural GPS?”